Electromagnetic proportional pressure control valve

Abstract

An electromagnetic proportional pressure control valve includes a housing, and a spool slidably received in the housing. The spool has a pair of first and second pressure receiving portions which are equal to each other in effective pressure receiving area. A primary pressure in a primary port is applied to the first pressure receiving portion, and a secondary pressure in a secondary port is applied to the second pressure receiving portion. A form due to the primary pressure acts on the spool in a direction to increase the secondary pressure, and a force due to the secondary pressure acts on the spool in a direction to decrease the secondary pressure. A force of a spring and a force of an electromagnetic actuator also act on the spool in the opposite directions. A variation in the primary pressure directly appears in the secondary pressure.

What is claimed is: 
     
       1. An electromagnetic proportional pressure control valve comprising: (a) housing means having an elongated guide hole having an inner peripheral surface, a primary port, a secondary port and a discharge port, said three primary, secondary and discharge ports communicating with said guide hole and being spaced from one another along the length of said guide hole, said secondary port being disposed between said primary port and said discharge port;   (b) a spool received in said guide hole for movement along said guide hole between a first position where said secondary port is out of communication with said primary port and is in communication with said discharge port and a second position where said secondary port is in communication with said primary port discharge port and is out of communication with said discharge port, said spool comprising first pressure receiving means and second pressure receiving means which are equal to each other in pressure receiving area, a primary pressure in said primary port being applied to said first pressure receiving means and a secondary pressure in said secondary port being applied to said second pressure receiving means, a force due to said primary pressure being exerted in a first direction to move said spool from said first position to said second position, and a force due to said secondary pressure being exerted in a second direction to move said spool from said second position to said first position;   (c) spring means urging said spool in one of said first and second directions; and   (d) an electromagnetic actuator for applying an electromagnetic force to said spool so as to move said spool in the other of said first and second directions, said electromagnetic force being proportional to the magnitude of an electric current supplied to said electromagnetic actuator; wherein said spool comprises a first land portion and a second land portion, said first land portion cooperating with the portion of the inner peripheral surface of said guide hole disposed between said primary port and said secondary port so as to control the communication between said primary and secondary ports, said second land portion cooperating with the portion of the inner peripheral surface of said guide hole disposed between said secondary port and said discharge port so as to control the communication between said secondary port and said discharge port, said first and second land portions constituting said second pressure receiving means, said first land portion having a diameter greater than that of said second land portion and the effective pressure receiving area of said second pressure receiving means being determined by the difference in area between pressure receiving areas of said first and second land portions.     
     
     
       2. An electromagnetic proportional pressure control valve according to claim 1, in which said electromagnetic force of said electromagnetic actuator moves said spool in said first direction, the force of said spring means being applied to said spool in said second direction. 
     
     
       3. An electromagnetic proportional pressure control valve according to claim 2, in which spring seat means is mounted on said spool, said housing means having a spring seat portion, and said spring means comprising a compression coil spring wound around said spool and acting between said spring seat means and said spring seat portion. 
     
     
       4. An electromagnetic proportional pressure control valve according to claim 3, in which said spring seat means comprises an annular spring seat mounted on the outer periphery of said spool. 
     
     
       5. An electromagnetic proportional pressure control valve according to claim 3, in which a through hole is formed diametrically through said spool and passes through the axis of said spool, said spring seat means comprising an elongated straight spring seat which is loosely passed through said through hole with its opposite ends projected from the outer peripheral surface of said spool, one end of said coil spring being received by said opposite ends of said spring seat, said spool having a support portion provided centrally of the length of said through hole and extending into said through hole, said support portion being disposed on that side of said spring seat facing away from said coil spring, said spring seat being held at its central portion against said support portion, the resilient force of said coil spring being concentrated on said support portion via said spring seat. 
     
     
       6. An electromagnetic proportional pressure control valve according to claim 5, in which said spool has another hole formed therein and perpendicularly intersecting said through hole at the axis of said spool, a cylindrical support pin being receiving in said another hole and fixed thereto, part of the peripheral surface of said support pin being projected into said through hole at the axis of said spool so as to serve as said support portion, and said spring seat having a cylindrical shape and held in point-contact with said support portion. 
     
     
       7. An electromagnetic proportional pressure control valve according to claim 1, in which said housing means includes a pair of first and second pilot chambers spaced from each other along the axis of said guide hole, said first pilot chamber being disposed at one end of said guide hole close to said primary port, said second pilot chamber being disposed at the other end of said guide hole close to said discharge port, said primary pressure being fed to said first and second pilot chambers, the opposite ends of said spool being exposed respectively to said first and second pilot chambers so as to receive said primary pressure, thus constituting said first pressure receiving means, one end of said spool exposed to said first pilot chamber being greater in pressure receiving area than the other end of said spool exposed to said second pilot chamber, and the effective pressure receiving area of said first pressure receiving means being substantially determined by the difference between the pressure receiving areas of said opposite ends of said spool. 
     
     
       8. An electromagnetic proportional pressure control valve according to claim 7, in which said pair of pilot chambers communicate with said primary port via communication passage means. 
     
     
       9. An electromagnetic proportional pressure control valve according to claim 8, in which said communication passage means includes a first passage formed in said spool, said primary pressure in said primary port being fed to said second pilot chamber via said first passage. 
     
     
       10. An electromagnetic proportional pressure control valve according to claim 9, in which said first passage formed in said spool has an axial hole and a first hole, said axial hole extending along the axis of said spool and opening at its one end to the other end of said spool to be exposed to said second pilot chamber, said first hole being formed through a peripheral wall of said spool and communicating at one end with said axial hole, and the other end of said first hole opening to the outer peripheral surface of said spool and communicating with said primary port. 
     
     
       11. An electromagnetic proportional pressure control valve according to claim 10, in which said communication passage means further includes a second passage formed in said housing means, said spool having a second hole formed through the peripheral wall thereof, said second hole communicating at one end with said axial hole and opening at the other end to the outer peripheral surface of said spool to communicate with said second passage, and said primary pressure in said primary port being fed to said first pilot chamber via said first hole, said axial hole, said second hole and said second passage. 
     
     
       12. An electromagnetic proportional pressure control valve according to claim 10, in which said axial hole of said spool is open at the other end to the one end of said spool to be exposed to said first pilot chamber, so that said primary pressure in said primary port is fed to said first pilot chamber via said first hole and said axial hole. 
     
     
       13. An electromagnetic proportional pressure control valve according to claim 8, in which said communication passage means includes a first passage and a second passage both of which are formed in said housing means, said primary port communicating with said first pilot chamber via said first passage, and said primary port communicating with said second pilot chamber via said second passage. 
     
     
       14. An electromagnetic proportional pressure control valve according to claim 13, in which one end portion of said guide hole disposed close to said primary port serves as a pressure introduction chamber, said primary pressure in said primary port being fed to said pressure introduction chamber via said second passage, said spool having a third land portion disposed in sliding contact with that portion of the inner peripheral surface of said guide hole disposed between said pressure introduction chamber and said primary port in such a manner that a narrow clearance is formed between said third land portion and said that portion of the inner periphery of said guide hole, said third land portion being equal in diameter to said first land portion, said third land portion having a first annular groove formed in the outer periphery thereof, said first annular groove communicating with said discharge port via a third passage formed in said spool, said third land portion also having a second annular groove and a third annular groove both of which are formed in the outer periphery thereof and disposed respectively on the opposite sides of said first annular groove, said second annular groove being spaced from said first annular groove toward said pressure introduction chamber, said third annular groove being spaced from said first annular groove toward said primary port, and a fluid of said primary pressure in said pressure introduction chamber and said primary port flowing via said narrow clearance to said first annular groove subjected to a relatively low pressure, so that the fluid under high pressure is stored in said second and third annular grooves. 
     
     
       15. An electromagnetic proportional pressure control valve according to claim 14, in which said third passage in said spool has an axial hole extending along the axis of said spool, a first hole and a second hole, said first and second holes being formed through the peripheral wall of said spool, said first hole communicating at one end with said axial hole and communicating at the other end with said first annular groove, and said second hole communicating at one end with said axial hole and opening at the other end to the outer periphery of said spool to communicate with said discharge port. 
     
     
       16. An electromagnetic proportional pressure control valve according to claim 15, in which said pressure introduction chamber serves as a chamber for accommodating said spring means therein.